Topically administered active substances are mainly used to treat the redness, swelling, itching and discomfort of psoriasis, atopic dermatitis and other pathologies of the skin. The majority of such active drug substances exhibit poor solubility in standard solvents, such as water. Poor solubility in the context of this application means that the solubility of the compound in water is 20 mg/l or less at 20° C. Glucocorticosteroids, steroids, calcineurin inhibitors, vitamin D analoques, retinoids, immunosuppressants, antimycotics, antiinfectives, estrogens, androgens, fumaric acid esters are typical drug classes for topical administration with such low water solubility. Other examples for such poorly soluble compounds are provided e.g. in WO 03/082827 or WO 2006/050998. One example is the non-steroidal active substance having the chemical name (R)-1,1,1-Trifluoro-4-(5-fluoro-2,3-dihydrobenzofuran-7-yl)-4-methyl-2-{[(2-methyl-5-quinolyl)amino]methyl}pentan-2-ol, the empirical formula of which is C25H26F4N2O2, having a molecular weight of 462.5. This is the compound according to example 1 of WO 2006/050998 (hereinafter Ex1/998). Said compound is a crystalline, non-polymorphic yellowish-to-green powder that is insoluble in water, only slightly soluble in hexane and moderately soluble in ethyl alcohol. It has very poor solubility in standard cream and ointment vehicles being in use for the topical administration, such as petrolatum and mineral oils.
Commercially, topically administered drug products are available as solutions, suspensions, creams and ointments. U.S. Pat. No. 3,892,856 describes the use of corticosteroids dissolved in polyethylene glycol and emulsified into an oleaginous base. Another option to present poorly water-soluble compounds for patient use is the formulation of an oil-in-water type formulation containing the active compound in suspended form.
Other examples can be found in the scientific and patent literature.
It was the object of the present invention to provide a formulation containing the drug substance at a concentration of at least 0.1% in dissolved state in order to achieve an increased in vitro release rate and a higher efficacy in vivo.